Our long term aims are to clarify the genetic basis of hematopoietic malignancies and the role of proto-oncogenes in hematopoiesis by characterizing transgenic mice bearing oncogenes. Diverse lymphoid neoplasms have been modelled through mice bearing the myc, N-myc, v-abl, bcr-v-abl, N-ras or bcl-2 gene linked to an immunoglobulin enhancer. Pertinent recent findings include the ability of bcl-2 to protect both B and T cells from programmed cell death (apoptosis), generation of novel B lymphoid/macrophage progenitor tumors by myc plus bcl-2, and identification by insertional mutagenesis of bmi- 1, a collaborator of myc. In the next three years, critical issues in lymphoid neoplasia will be addressed using these strains and novel lymphomagenic lines bearing the max, bmi-1 and cyclin D1 genes. To extend this approach to other forms of leukemia, a pan-hematopoietic transgenic vector will be developed. 1. Programmed cell death. Since apoptosis has a central role in development, homeostasis and neoplasia, the genetic pathways to cell death will be explored by introducing the bcl-2 transgene into mutant mice lacking the pathways regulated by either the Fas surface receptor or the pS3 tumor suppressor. The sub-cellular localization of Bcl-2 will be clarified and collaboration of bcl-2 with other oncogenes will be explored. 2. Oncogenic partners of myc. The importance of myc in tumorigenesis has prompted studies on genes that abet its function: bmi-1 and max, which encodes a protein that associates with Myc. Their potential to cooperate with myc in lymphomagenesis will be determined, the unusual Bmi-1 nuclear localization explored and the markedly perturbed hematopoiesis in one max line investigated. 3. Cyclin D1 (bcl-1). Since cyclins may link signal transduction pathways with cell cycle control and the cyclin D1 gene is a prime candidate oncogene, its impact on lymphoid growth control, cell cycle status, differentiation and oncogenicity is under study. 4. Oncogene cooperativity with the p53 tumor suppressor. To explore tumorigenesis when p53 function has been abrogated, lymphomas of transgenic strains will be screened for alterations of the p53 gene or the p53 regulator mdm-2, and the myc and N-ras transgenes will be introduced into a p53 null background. 5. Pan-hematopoietic vector. Since the vav gene is expressed in all hematopoietic but not other cell types, the ability of its promoter to drive pan-hematopoietic expression in vivo will be tested with a reporter gene and, if successful, with the bcr-abl and bcl-2 genes to generate models of myeloid leukemia. Significance. This highly productive project is generating unique animal models for delineating pathways to hematopoietic malignancies. It should help to clarify how oncogenes influence differentiation, cell cycle status, and apoptosis, and reveal how oncogenes work together, collaborate with loss of tumor suppressors and intersect control of the cell cycle.